This invention relates to an exchangeable lens for use in an internal light-measuring type single lens reflex camera, and more particularly to an exchangeable lens for use in a camera which is equipped with a diaphragm-priority-automatic-shutter-speed control mechanism for automatically controlling the shutter speed, and a shutter-speed-priority-automatic-diaphragm control mechanism for automatically controlling the aperture.
With a prior art camera equipped with a diaphragm-priority-automatic-shutter-speed control mechanism alone, in case diaphragm-priority-automatic-shutter-speed control is effected, the transmission of only the step-difference between the fully open aperture value and the set aperture value for an exchangeable lens enables the automatic control of the shutter speed. The set aperture value is indicated by indicating means adapted to operate from the direct introduction of light into the finder through an optical system.
In a camera equipped with shutter-speed-priority-automatic diaphragm control and diaphragm-priority-automatic-shutter-speed control mechanisms, the fully open aperture value should be transmitted from the lens to the camera for indicating the aperture value to be set at the time of photographing, when using shutter-speed-priority-automatic-diaphragm control.
If only one kind of an exchangeable lens is used, the transmitting means therefor may be readily provided. However, there are different kinds of exchangeable lenses in the market. In addition, even standard lenses having varying maximum aperture values are on the market (Standard lens . . . 50 mm: F1.2, F1.4, F1.7 and the like).
As a result, there have been attempts to provide a transmitting member having a different configuration on the flat joint lens surface, which is coupled to the camera body, commensurate with the fully open aperture value of each exchangeable lens. An information-receiving member is provided on the flat surface of the camera body which is coupled to the lens, so that information of the fully open aperture value is transmitted to the side of the camera. With this arrangement, a transmitting member projects from the flat joint surface on the lens, so that such an exchangeable lens cannot be used in a prior art camera that does not have a shutter-speed-priority-automatic-diaphragm control mechanism.
However, because of the complexity of the construction of a camera it is quite difficult to provide an information-receiving member on the flat joint surface of the camera body that projects therefrom, resulting in design difficulties. Even if such a transmitting means is provided on the flat joint surface between the camera body and a lens, a dimensional error would be incurred when the transmitting means is mounted. It is well known that such a dimensional error, if any, is a critical problem in the manufacture of cameras.